The process of the present invention relates to the recovery of hydrocarbons from a subterranean formation of heavy oil containing sand and in particular to the recovery of hydrocarbons by simultaneously injecting steam, gas and hydrocarbon diluent along an established communication zone in the formation and producing a formation fluid therefrom.
Heavy oil containing sands are sands saturated with crude petroleum or bitumen of high viscosity which cannot be recovered by conventional petroleum recovery methods. Under reservoir conditions, the bitumen or heavy oil in the sands cannot be made to flow with any practical pressure gradient. An in situ process for the recovery of bitumen has a goal to reduce the viscosity of the bitumen thereby making it more amenable to flow. At reservoir temperature bitumen has a viscosity of several million centipoise, however, in raising the temperature to 300.degree. F., the viscosity is reduced to about 35 centipoise and at 400.degree. F. is reduced to 5 to 10 centipoise.
It has been long recognized to utilize steam as an agent to achieve a hot drive for the recovery of hydrocarbons from formations of heavy oil containing sand. Usually a communication zone, that is a permeable pathway, is established between at least two wells penetrating the heavy oil containing sand formation. Communication zones may exist as naturally occurring permeable strata or may be established by conventional methods of hydraulic fracturing and propping. The steam is injected through one well at high temperature and pressure, passes through the communications zone, transferring sufficient heat to the heavy oil containing sands to lower the viscosity of the bitumen or heavy oil, and drives a steam-steam condensate-heavy oil mixture to be produced at the second well.
More recently, additives have been used to improve recovery from heavy oil containing sand. These additives usually work in one of two ways. Increased drive energy can be provided in the reservoir by using additives which dissolve in the formation fluids at the pressures and temperatures of injection, but flash from the fluids as the pressure is reduced to provide a solution-gas drive. Additives such as low molecular weight hydrocarbons, carbon dioxide, nitrogen and oxygen have been suggested for use in the past.
Additives are also used to provide a solvent effect. In this case, the additive dissolves in the bitumen to reduce the viscosity and improve fluid transmissibility within the formation. Suitable solvents include C.sub.6 linear or aromatic compounds, multiple ring aromatics, naphtha, and volatile solvents such as carbon disulphide and toluene.
A number of prior art patents disclose these additives being combined with the steam recovery of bituminous sand.
Redford, in U.S. Pat. No. 3,908,762, discloses the use of steam together with a non-condensible gas such as carbon dioxide, air or nitrogen in a recovery process in order to expand an established communication zone.
Barry, in U.S. Pat. No. 3,881,550, suggests injecting steam with a hot solvent such as depentanized naphtha into the formation and recoverying a fluid-bitumen mixture from a remotely located well. However, steam-solvent recovery systems have, in the past, required large quantities of relatively expensive solvents to be injected into the formation. Usually volumes in the order of 10-40% per pound of steam have been used.
Multi-additive systems have been proposed for use with steam recovery wherein solvent and gas are added together to pre-condition the reservoir in a soak shut-in period before injecting steam to effect recovery. U.S. Pat. Nos. 4,004,636, to Brown et al and 4,026,358, to Allen disclose such systems.
To our knowledge it is not a known process to utilize the advantages of steam, gas and solvent in an additive manner by injecting the three components simultaneously into a bituminous formation.